Merge pull request #2 from sdc-ad/features/end_of_transaction_event

Emit event when reaching end of event stream transaction

src/AppCoreNet.EventStore.Abstractions/EventTransactionCommittingEvent.cs

@@ -0,0 +1,11 @@
+namespace AppCoreNet.EventStore
+{
+    /// <summary>
+    /// An event which is emitted before the transaction processing the event queue is committed.
+    /// This allows listeners to ensure any buffered work is completed before the transaction is committed.
+    /// </summary>
+    [EventType(nameof(EventTransactionCommittingEvent))]
+    public class EventTransactionCommittingEvent
+    {
+    }
+}

src/AppCoreNet.EventStore/Subscriptions/SubscriptionService.cs

@@ -139,6 +139,30 @@ await listener.HandleAsync(watchResult.SubscriptionId, @event, cancellationToken
                     }
                 }
 
+                try
+                {
+                    await listener
+                        .HandleAsync(
+                            watchResult.SubscriptionId,
+                            new EventEnvelope(new EventTransactionCommittingEvent()),
+                            cancellationToken)
+                        .ConfigureAwait(false);
+                }
+                catch (Exception ex)
+                {
+                    _logger.LogError(ex, "Error completing event transaction. This action will be retried.");
+
+                    if (transaction != null)
+                    {
+                        await transaction.RollbackAsync()
+                                         .ConfigureAwait(false);
+                        await transaction.DisposeAsync()
+                                         .ConfigureAwait(false);
+                    }
+
+                    continue;
+                }
+
                 await subscriptionStore.UpdateAsync(watchResult.SubscriptionId, lastPosition, cancellationToken)
                                        .ConfigureAwait(false);